The Bottle Cutter from Creators Stained Glass is simple to use and makes exact cuts around the bottle. Constructed from a polycarbonate plastic, durable stainless steel slide bars and enclosed ball bearing rollers (to keep out glass slivers). Simply set the cutting wheel to exact spot on the attached ruler, tighten the wheel to hold the cutter in place, then simply spin the bottle on the rollers while applying pressure.
As a special bonus, also included is a Palm Protector that allows the bottle to spin easily while keeping your hands safe while cutting (see picture below).